1. Field of the Invention
The present invention is directed to a method of improving performance of wideband Raman amplifiers.
2. Description of Related Art
Optical transmission systems that maximize fiber transmission capacity require the use of C-, L-, and, possibly, S-bands simultaneously. In order for these systems to support high data rates and long reach, the use of Raman amplification is virtually mandatory, especially for S-band. Until recently, the bulk of research regarding Raman amplifiers and Raman amplification has been directed toward generation of broader and flatter Raman gain, as well as providing gain in new wavelength windows. In particular, cascaded Raman effect has been widely exploited, where an efficient pump power transfer by about one Stokes shift toward longer wavelength, is repeated several times to improve Raman gain performance.
Further modification of this cascading method has been proposed in U.S. Pat. No. 6,239,902 and U.S. Pat. No. 6,239,903 to Islam et al. These references teach broadening of the Raman pump spectrum by positioning one of the intermediate Raman orders near zero-dispersion wavelength λ0 to subsequently transfer the broadened spectrum by one or more Stokes shift toward longer wavelengths. This broadening of the Raman pump spectrum occurs due to an effect known in literature as four-wave-mixing, parametric amplification, or modulation instability.